A storage device which includes a backup power supply and a backup memory and which has a function of storing data on a cache that stores I/O data to a disk in the backup memory in the event of power-cut is known. Moreover, in a processing sequence during the occurrence of power-cut, write-out of logs (fault information or the like) accumulated on a memory is also performed.    [Patent Literature 1] Japanese Laid-open Patent Publication No. 2005-293085    [Patent Literature 2] Japanese Laid-open Patent Publication No. 2008-77669
However, in such a conventional storage device, when a cache size increases with an increase in the size of a mounted memory, the time (write-out time) required for writing out data of the cache to the backup memory increases.
On the other hand, since the capacity of a backup power supply is limited, when the time required for writing out cache data increases, the time allocatable to the log write-out process decreases. Thus, there is a problem in that writing out logs on a memory needs to be performed in a short time.